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A 26-year-old man was given trimethoprim-sulfamethoxazole for sinusitis and broke out in hives 1 week later. The hives were all over his trunk and arms (Figures 150-1 and 150-2). He had no airway compromise and had only urticaria without angioedema. His sinus symptoms were mostly resolved, so he was told to stop the antibiotic and take an oral antihistamine. The H1-blocker gave him relief of symptoms and the wheals disappeared over the next 2 days.

Figure 150-1

A 26-year-old man with acute urticaria due to trimethoprim-sulfamethoxazole. (Courtesy of Richard P. Usatine, MD.)

Figure 150-2

Note the confluence of wheals with a well-demarcated border on the arm of the man with acute urticaria due to trimethoprim-sulfamethoxazole. (Courtesy of Richard P. Usatine, MD.)

Urticaria and angioedema are a heterogeneous group of diseases that cause swelling of the skin and other soft tissues. They both result from a large variety of underlying causes, are elicited by a great diversity of factors, and present clinically in a highly variable way.1 Standard hives with transient wheals is the most common manifestation of urticaria.


  • It is estimated that 15% to 25% of the population may have urticaria sometime during their lifetime.2
  • Urticaria affects 6% to 7% of preschool children and 17% of children with atopic dermatitis.2
  • Among all age groups, approximately 50% have both urticaria and angioedema, 40% have isolated urticaria, and 10% have angioedema alone.2
  • Acute urticaria is defined as less than 6 weeks' duration. A specific cause is more likely to be identified in acute urticaria.2
  • The cause of chronic urticaria (>6 weeks' duration) is determined in less than 20% of cases.2
  • Chronic urticaria is twice as common in women as in men.3
  • Chronic urticaria predominantly affects adults.3
  • Up to 40% of patients with chronic urticaria of more than 6 months' duration still have urticaria 10 years later.3

  • The pathophysiology of angioedema and urticaria can be immunoglobulin (Ig) E mediated, complement mediated, related to physical stimuli, autoantibody mediated, or idiopathic.
  • These mechanisms lead to mast cell degranulation resulting in the release of histamine. The histamine and other inflammatory mediators produce the wheals, edema, and pruritus.
  • Urticaria is a dynamic process in which new wheals evolve as old ones resolve. These wheals result from localized capillary vasodilation, followed by transudation of protein-rich fluid into the surrounding skin. The wheals resolve when the fluid is slowly reabsorbed.
  • Angioedema is an edematous area that involves transudation of fluid into the dermis and subcutaneous tissue (Figures 150-3 and 150-4).

Figure 150-3

Young black woman with angioedema after being started on an angiotensin-converting enzyme (ACE) ...

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